@manjuvenamma --
I have never been able to achieve this in linear mode, but in professional (WYSIWYG) mode, enter your matrix. Then highlight the entire matrix and use one of the Bracket options on the Design menu. Hope this works for you.
How does one insert bold oblique (ie, not italic) capital letters to represent matrices within equations? I found one reference to the style function within EE (with which I'm familiar in pre-W2007 EE), but was unable to locate it in the 2007 version. Murray Sargent III's 2006 reference work...